U.S. Pat. No. 2,715,359 describes a fume hood with a laterally slidable sash. A room air vent is shown directly below this sash, and air flow through the room air vent is controlled by the vertically movable damper as shown in FIG. 4. The vertically movable damper is actuated by the horizontal sash movement through a complicated linkage of sprockets, chains, and counterweights. Any slippage of the sprocket could cause the damper to bind in the tracks at each end of the damper.
U.S. Pat. No. 3,604,333 also shows a fume hood with a horizontally slidable sash connected to dampers 26a, 26b, and 26c directly above the sash. These dampers control the flow of auxiliary air, not room air. Also, these dampers operate in direct relationship with the sash. When the sash is open, the damper is open; and conversely, when the sash is closed, the damper is closed. Because of this direct relationship of movement between the horizontally movable sash and the horizontally movable damper, a complicated duct work is needed for handling the auxiliary air. This is noted by the expensive duct work and housing behind the dampers, as well as in front of the dampers. There is no showing that the dampers in this patent have anything to do with the vent of room air directly into the hood.